text: In one application the asymmetry in an atropisomer is transferred in a chemical reaction to a new stereocenter. The atropisomer is an iodoaryl compound synthesised starting from (S)-valine and exists as the (M,S) isomer and the (P,S) isomer. The interconversion barrier between the two is 24.3 kcal/mol (101.7 kJ/mol). The (M,S) isomer can be obtained exclusively from this mixture by recrystallisation from hexanes. The iodine group is homolytically removed to form an aryl radical by a tributyltin hydride/triethylboron/oxygen mixture as in the Barton–McCombie reaction. Although the hindered rotation is now removed in the aryl radical, the intramolecular reaction with the alkene is so much faster than is rotation of the carbon–nitrogen bond that the stereochemistry is preserved. In this way the (M,S) isomer yields the (S,S) dihydroindolone.
  The most important class of atropisomers are biaryls such as diphenic acid, which is a derivative of biphenyl with a complete set of ortho substituents. Heteroaromatic analogues of the biphenyl compounds also exist, where hindered rotation occurs about a carbon-nitrogen or a nitrogen-nitrogen bond. Others are dimers of naphthalene derivatives such as 1,1'-bi-2-naphthol. In a similar way, aliphatic ring systems like cyclohexanes linked through a single bond may display atropisomerism provided that bulky substituents are present. The use of axially chiral biaryl compounds such as BINAP, QUINAP and BINOL, have been found to be useful in the area of asymmetric catalysis as chiral ligands.
  Their ability to provide stereoinduction has led to use in metal catalyzed hydrogenation, epoxidation, addition, and allylic alkylation reactions. Other reactions that can be catalyzed by the use of chiral biaryl compounds are the Grignard reaction, Ullmann reaction, and the Suzuki reaction. A recent example in the area of chiral biaryl asymmetric catalysis employs a five-membered imidazole as part of the atropisomer scaffold.  This specific phosphorus, nitrogen-ligand has been shown to perform enantioselective A-coupling.